For legal and official purposes, evidentiary documents and other official documentation are usually required to be in the official language(s) of jurisdiction. In certain countries, it is required for the translator to swear an oath to attest that the document translated is the legal equivalent of the source text. Often, only a certain category of translators is authorized to swear such oaths. Occasionally translations are only accepted as the legal equivalent if accompanied by the original document or a sworn/certified copy.  Even if a translator is specialized in legal translations or is a lawyer in his country, it does not necessarily make him a sworn translator. The procedure for translating documents to legal equivalents is country-specific.

You can find more information relating to this under the heading of “Certified translation”